Electrically driven, self-contained in-tank gear rotor or gerotor fuel pumps have been used extensively for delivering fuel from a supply tank to an internal combustion engine of a motor vehicle or water craft. This type of pump produces a steady, non-surging, relatively highly pressurized flow of fuel over a relatively wide speed range, making it ideal for use with modern fuel injection systems. The design is also highly tolerant of fuel supply line pressure transients commonly associated with the abrupt opening and closing of individual fuel injectors.
Typically these pumps consist of a housing having a direct current electric motor with stationary, field-generating permanent magnets retained in place against a cylindrical flux tube by spring clips mounted in the housing, and a wound armature journalled for rotation in the housing and coupled to a gerotor pump assembly. Examples of various types of improvements in such pump constructions are shown in U.S. Pat. Nos. 4,352,641; 4,401,416; 4,500,270; 4,596,519; 4,697,995; 5,122,039; 5,248,223 and 5,411,376 all assigned to the assignee of record herein, Walbro Corporation of Cass City, Mich., and incorporated herein by reference. Although the gerotor fuel pumps disclosed in most of the above noted patents have enjoyed substantial commercial acceptance and success, improvements remain desirable. One problem lies in the difficulty and the complexity of fastening and aligning the inlet end cap, cam ring, outlet port plate and gerotor components during assembly of the pump. In gerotor pumps of the fixed face clearance (FFC) type these components must be precision machined to precise axial and radial dimensions to establish appropriate tolerance limits for the desired axial and radial clearances between the moving and stationary parts of the pump in order to optimize pump performance and efficiency. The parts must be securely and accurately axially clamped together in assembly and also accurately angularly aligned for proper registry of the inlet and outlet ports with the angular operational orientation of the inner and outer rotors of the gerotor pump. Typically, when it is desired to provide the pump as a unitary, operative subassembly, the clamping together of the pump components in assembly is accomplished by mounting bolts or cap machine screws threaded through corresponding aligned threaded holes in the inlet cover plate or cap, gerotor cam ring and outlet port plate. Two, three or even four of fastening such screws are typically provided, as well illustrated in U.S. Pat. No. 4,978,282. However, because it has not been economically feasible to achieve precision angular inter-alignment by using such threaded clamping screws or fasteners and associated threaded mounting holes, it is also customary to provide one or more precision formed and ground unthreaded alignment pins and precision finished unthreaded alignment bores in one or both of the end plates and cam ring to thereby establish accurate angular orientation of the pump components during assembly. The provision of both such sets of fastener screws and alignment pins, of course, adds cost to the pump assembly in both the manufacture and assembly of these pump components.
Another type of gerotor pump disclosed in several of the above noted patents is of the "zero clearance" type is which the gerotor components and associated cam ring are resiliently biased against one of the pump end plates by various forms of spring constructions including spring-type valve plates. Although such zero clearance type pumps are highly efficient from the manufacturing and performance stand point, if operated with contaminant-laden fuel, particularly "dry-fuel" of low lubricity, and driven to develop output pressures exceeding their normal ratings, such pumps can suffer undue wear and loss of efficiency and hence reduction in acceptable performance and operational life. Such adverse operational conditions can be encountered, for example, in certain marine engine applications often requiring fuel system delivery pressures in the order of 90 psi versus the typical 30-60 psi pump output pressures required of standard fuel pumps for use with automotive fuel injection systems FFC type gerotor pumps can more readily achieve such higher output pressures, but undue wear remains a problem, albeit less so, even with this type of pump under such adverse conditions.
Another problem encountered with in-tank fuel pumps under adverse shock and vibration conditions is the loosening of the motor field permanent magnets from their spring finger retention, as when so mounted in the pump housing or casing as shown in the above noted U.S. Pat. Nos. 4,352,641 and 5,000,270. Typically a special stop protuberance configuration is provided in the material of the pump inlet end cap or cam ring construction to serve as a fail-safe catch stop in the event of such loosening of the magnets so that the same can not be shaken to slip axially toward the pump structure and thus out of proper field alignment with the armature windings of the motor rotor. However, providing such geometry to the pump casing or pump inlet end cap construction or cam ring is not feasible in some applications, and in any event adds cost and weight to this pump part.